Gibberellins control Arabidopsis hypocotyl growth via regulation of cellular elongation
Journal of Experimental Botany
GA-signalling mutants of Arabidopsis, have provided insights into the mechanisms of GA action (Swain and The gibberellins (GAs) are endogenous regulators of Olszewski, 1996; Harberd et al., 1998; Ogas, 1998). plant growth. Experiments are described here that test However, the effects of GA on growth and development the hypothesis that GA regulates hypocotyl growth by have not been studied in Arabidopsis to the same extent altering the extent of hypocotyl cell elongation. These as have
... e as have GA-responses in other species. experiments use GA-deficient and altered GA-res-In this paper detailed investigations of the role played ponse mutants of Arabidopsis thaliana (L.) Heyhn. It is by GA in the regulation of Arabidopsis hypocotyl growth shown that GA regulates elongation, in both light-and are described. Arabidopsis hypocotyl elongation is often dark-grown hypocotyls, by influencing the rate and used as a model for the genetic analysis of signalling final extent of cellular elongation. However, light-and pathways, such as those for light and ethylene ( Whitelam dark-grown hypocotyls exhibit markedly different GA and Harberd, 1994; Ecker, 1995; von Arnim and Deng, dose-response relationships. The length of dark-grown 1996). Thus an improved understanding of the GAhypocotyls is relatively unaffected by exogenous GA, regulation of hypocotyl growth will add to the emerging whilst light-grown hypocotyl length is significantly picture of how plant growth is regulated via a complex increased by exogenous GA. Further analysis suggests network of internal and external factors. that GA control of hypocotyl length is close to satura- The Arabidopsis hypocotyl is of embryonic origin and tion in dark-grown hypocotyls, but not in light-grown is derived from the topmost of three cell layers, known hypocotyls. The results show that a large range of as the 'low lower tier', which are apparent at the early possible hypocotyl lengths is achieved via doseheart stage of embryogenesis (Jü rgens, 1994; Scheres dependent GA-regulated alterations in the degree of et al., 1994). As hypocotyl development proceeds, an elongation of individual hypocotyl cells. extra periclinal division occurs, adding a second cortical cell layer that is not found in the root. Numerous anti-Key words: Arabidopsis, cell elongation, gibberellin (GA), clinal divisions determine the final length and cellular GA mutants, hypocotyl. make-up of the pre-emergent hypocotyl (Scheres et al., 1994). References ga1 hypocotyls, and that exposure to PAC reduces the GA level in the ga1 hypocotyls still further. However, Chiang H-H, Hwang I, Goodman HM. 1995. Isolation of the Arabidopsis GA4 locus. The Plant Cell 7, 195-201. these observations could also be explained by effects of Downloaded from https://academic.oup.com/jxb/article-abstract/50/337/1351/530670 by guest on 27 July 2018 GAs regulate hypocotyl elongation 1357 Cowling RJ, Kamiya Y, Seto H, Harberd NP. 1998. Gibberellin alter the dose-response relationship of diverse gibberellin responses. Plant Physiology 119, 1199-1208. dose-response regulation of GA4 gene transcript levels in Arabidopsis thaliana. Plant Physiology 117, 1195-1203. Phillips AL, Ward DA, Uknes S, Appleford NEJ, Lange T, Huttly AK, Gaskin P, Graebe JE, Hedden P. 1995. Isolation Daykin A, Scott IM, Francis D, Causton DR. 1997. Effects of gibberellin on the cellular dynamics of dwarf pea internode and expression of three gibberellin-20-oxidase cDNA clones from Arabidopsis. Plant Physiology 108, 1049-1057. development. Planta 203, 526-535. Dolan L, Janmaat K, Willemsen V, Linstead P, Poethig S, Rademacher W. 1990. Inhibitors of gibberellin biosynthesis: applications in agriculture and horticulture. In: Takahashi N, Roberts K, Scheres B. 1993. Cellular organisation of the Arabidopsis thaliana root. Development 119, 71-84. Phinney BO, MacMillan J, eds. Gibberellins. New York: Springer-Verlag, 296-310. Ecker JR. 1995. The ethylene signal transduction pathway in plants. Science 268, 667-675. Reed JW, Foster KR, Morgan PW, Chory J. 1996. Phytochrome B affects responsiveness to gibberellins in Arabidopsis. Plant Ezura H, Harberd NP. 1995. Endogenous gibberellin levels influence in vitro shoot regeneration in Arabidopsis thaliana Physiology 112, 337-342. Sauter M, Mekhedov SL, Kende H. 1995. Gibberellin promotes (L.) Heynh. Planta 197, 301-305. Gendreau E, Traas J, Desnos T, Grandjean O, Caboche M, histone H1 kinase activity and the expression of cdc2 and cyclin genes during the induction of rapid growth in deepwater Höfte H. 1997. Cellular basis of hypocotyl growth in Arabidopsis thaliana. Plant Physiology 114, 295-305. rice internodes. The Plant Journal 7, 623-632. Scheres B, Wolkenfelt H, Willemsen V, Terlouw M, Lawson E, Harberd NP, King KE, Carol P, Cowling RJ, Peng J, Richards DE. 1998. Gibberellin: inhibitor of an inhibitor of ...? Dean C, Weisbeek P. 1994. Embryonic origin of the Arabidopsis primary root and root meristem initials.